The present disclosure generally relates to ferric chloride solutions, and more particularly, to processes for making stable ferric chloride solutions suitable for transport thereof, wherein the iron content in these solutions is about 16 to about 23 weight percent and does not precipitate at temperatures greater than −10° C.
Aqueous solutions of ferric chloride (FeCl3) are commonly used as flocculating agents for treatment of water, for hydrogen sulfide control, struvite control, sludge conditioning, color removal, phosphate removal, heavy metal removal, lime softening applications, and the like. For water treatment applications, the trivalent iron functions exceptionally well for both potable and wastewater clarification. Solutions containing ferric chloride can be prepared in a variety of ways. For example, ferric chloride solutions can be produced by oxidation of ferrous chloride using oxygen (O2) or chlorine (Cl2); by dissolution of ferric oxide with hydrochloric acid; and the like. These iron solutions are typically supplied with an iron concentration about 10 to about 14 weight percent because at iron concentrations greater than 15% by weight, precipitation can result especially when the ferric chloride solution is subjected to relatively low temperatures of about 0° C. or less.
Moreover, because many of the processes for manufacturing ferric chloride use hydrochloric acid as a reagent in the reaction, precipitation can result at even lower iron concentrations depending on the concentration of hydrochloric acid in the final ferric chloride solution. For example, the reaction of ferric oxide with hydrochloric acid to form ferric chloride can be quantified as follows:1Fe2O3+6HCl→2FeCl3+3 H2O
The hydrochloric acid and ferric oxide react to form reaction products including ferric chloride, water, and residuals including unreacted hydrochloric acid and unreacted ferric oxide. The amount of unreacted hydrochloric acid in the product is typically on the order of a few weight percent at most. As shown in prior art FIG. 1, the phase behavior at 0° C. of a ferric chloride, hydrochloric acid, and water system is such that the maximum iron content in solution decreases as a function of increasing hydrochloric acid up to an excess of about 15 weight percent hydrochloric acid.
In view of economies of scale, it would be desirable to maximize the amount of trivalent iron content available in ferric chloride solutions and provide high iron content ferric chloride solutions that are stable during transportation from one location to another location, especially if subjected to relatively low temperatures. Accordingly, it would be desirable and a significant commercial advantage to define a process and solution composition that provides a stable ferric chloride solution with increased iron content.